The present invention relates generally to real time positioning systems and, more particularly, to the use of such systems to control access to computer databases to assist in task scheduling.
Personal Digital Assistants (PDAs) have become more and more common in today""s society. The term PDA refers generally to mobile computer systems, typically handheld, which users employ for a variety of tasks such as storing telephone and address lists (databases), calendaring information, task (i.e., to-do) lists, etc. Some PDAs also incorporate a wireless communication link, allowing the unit to operate as a portable facsimile device, Internet access device and/or pager. Further, PDAs can be configured to operate with Global Positioning System (GPS) receivers as described in U.S. Pat. No. 5,528,248 to Steiner et al., entitled xe2x80x9cPersonal Digital Location Assistant Including a Memory Cartridge, A GPS Smart Antenna and a Personal Computing Devicexe2x80x9d assigned to the assignee of the present invention and incorporated by reference herein.
The GPS utilizes signals transmitted by a number of in-view satellites to determine the location of a GPS antenna which is connected to a receiver. Each GPS satellite transmits two coded L-band carrier signals which enable some compensation for propagation delays through the ionosphere. Each GPS receiver contains an almanac of data describing the satellite orbits and uses ephemeris corrections transmitted by the satellites themselves. Satellite to antenna distances may be deduced from time code or carrier phase differences determined by comparing the received signals with locally generated receiver signals. These distances are then used to determine antenna position. Only those satellites which are sufficiently above the horizon can contribute to a position measurement, the accuracy of which depends on various factors including the geometrical arrangement of the satellites at the time when the distances are determined.
Distances measured from an antenna to four or more satellites enable the antenna position to be calculated with reference to the global ellipsoid WGS-84. Local northing, easting and elevation coordinates can then be determined by applying appropriate datum transformation and map projection. By using carrier phase differences in any one of several known techniques, the antenna coordinates can be determined to an accuracy on the order of xc2x11 cm.
Although U.S. Pat. No. 5,528,248 describes how a GPS receiver can be integrated with a PDA to display navigation information for a user, it does not describe how positioning information provided to the PDA can be used in other ways.
According to one embodiment, a computer assisted method of scheduling tasks is provided. The method allows a task description to be stored in a database accessible by a mobile computer system. The mobile computer system receives positioning information corresponding to its geographic location and indexes the database based on the positioning information when the information indicates that the mobile computer system is in a geographic location that facilitates completion of a task associated with the task description.
The database may be resident in the mobile computer system or accessible in other ways, for example, via the Internet. The task description preferably includes a geocode which corresponds to the geographic location at which completion of the task may be facilitated. The task description may also include textual, voice or other messages which can be displayed and/or played back to a user. The positioning information may be obtained from a GPS satellite, a GLONASS satellite or a pseudolite. The mobile computer system may be a portable unit, such as a PDA, or integrated within a vehicle.
A second embodiment provides a computer assisted method of using a geocoded database. In this embodiment, a mobile computer system is transported to a first location having first geographic coordinates at a first time. At the first location, RF signals which contain information indicative of the location of a source of their transmission are received and processed to derive the geographic coordinates of the first location. The geographic coordinates of the first location are associated with a descriptor indicative of the first location in a database associated with the mobile computer system so as to form a geocoded entry in the database and a task to be accomplished at the first location is similarly associated with the geocoded entry in the database.
The mobile computer system is transported to a second location at a second time and RF signals containing information indicative of the source of the signals are received and processed to determine the geographic coordinates of the second location. The geographic coordinates of the second location are analyzed to determine whether the second location is within a predetermined range of the first location and, if so, a user is alerted. The user may be alerted by displaying an alert message, such as a task description corresponding to the task to be accomplished at the first location, on a display associated with the mobile computer system.
A further embodiment provides a mobile computer system having a location determination unit configured to receive and process RF signals containing information indicative of the location of a source of the signals, a database coupled to the location determination unit and including location coordinates indicative of a location of interest and a database interface unit configured to access the database according to the location of the mobile computer system.